如何调试ROM中存在的代码？

Question

I wanna know if normal practice of setting the breakpoints, step-in & step-out works same for the code which reside on ROM also. Do we have to do something extra for ROM debugging.

Answer 1

It will depend largely on the processor an the debug hardware you use. Many microcontrollers include on-chip debug hardware that includes hardware breakpoints that are essentially program-counter comparators. Other facilities may be supported such as data access break-points and instruction trace - essentially an on-chip in-circuit emulator (ICE).

Hardware breakpoints are a necessarily limited resource; for example ARM7 devices have just two while ARM Cortex-M3/4 are endowed with eight.

Either way, to utilise on-chip debug you require suitable debugger hardware (often via JTAG, or a vendor proprietary interface) to interface the target to the host debugger software.

For chips without on-chip debug, you typically use an in-circuit emulator. This is debug hardware that connects to the target board in place of the processor and can be controlled directly by the host debug software. The emulator hardware executes instructions identically to the actual processor but can be halted and stepped and have breakpoints set. Essentially the ICE works like a special version of the target processor with debug support. A true ICE is uncommon on modern processors since on-chip debug capabilities are almost ubiquitous even on small devices such as PIC and AVR, however some external debug hardware can support features not available on on-chip debug. For example Segger's J-Link supports unlimited break-points on ARM7 and Cortex-M3/4.